1. Field of the Invention
The invention relates to a battery pack, a power source apparatus, and a charging and discharging method, in which a parallel construction and a serial construction of a plurality of secondary batteries can be switched by using switching circuits.
2. Description of the Related Art
A construction such that a plurality of secondary batteries which can be charged and used again are serially arranged and used as a power source of electronic equipment is generally known. In this instance, there is a case where characteristics of a plurality of secondary batteries which are serially arranged, for example, capacities of the secondary batteries are different. If the secondary batteries having different characteristics are charged in a state where they are serially arranged, the secondary battery which is not fully charged or the secondary battery which is overcharged is caused. It is difficult to charge a plurality of secondary batteries arranged serially in this state as mentioned above. A tendency such that the characteristics of the secondary batteries are different becomes more remarkable as the secondary batteries are deteriorated.
Therefore, a method whereby a plurality of secondary batteries which are serially arranged are charged one by one and all of the secondary batteries are fully charged has been proposed as disclosed in JPA-4-248332. For example, as shown in FIG. 1, there is a method of charging two secondary batteries E51 and E52 which are serially arranged one by one. In case of charging the secondary battery E51 by a charging device Rc, switching circuits S51 and S53 are turned on and switching circuits S52 and S54 are turned off. In case of charging the secondary battery E52 by the charging device Rc, the switching circuits S51 and S53 are turned off and switching circuits S52 and S54 are turned on.
Further, a method of charging four secondary batteries E61, E62, E63, and E64 one by one will be described with reference to FIG. 2. To charge the four secondary batteries E61, E62, E63, and E64, respectively, a voltage current is outputted from a charging device Re. For example, when switching circuits S61 and S65 are turned on, the secondary battery E61 is charged and when switching circuits S62 and S66 are turned on, the secondary battery E62 is charged. When switching circuits S63 and S67 are turned on, the secondary battery E63 is charged and when switching circuits S64 and S68 are turned on, the secondary battery E64 is charged.
As shown in FIG. 3A, a voltage current is supplied from an input terminal Ti70. When only a switching circuit S77 is turned on, a secondary battery E71 is charged. When switching circuits S74 and S78 are turned on, a secondary battery E72 is charged. When switching circuits S75 and S79 are turned on, a secondary battery E73 is charged. When only a switching circuit S76 is turned on, a secondary battery E74 is charged. In case of discharging from an output terminal To, switching circuits S71, S72, and S73 are turned on as shown in FIG. 3B.
However, when a plurality of secondary batteries which are serially arranged are charged, since they are charged one by one, there is a problem such that it takes a time until all of the secondary batteries are fully charged.